Not Applicable.
Not Applicable.
A known method for the planarization of semi-conductor wafers in the semi-conductor industry is the so-called CMP process. This is a chemical-mechnical machining by means of a fluid (slurry), with the chemically reactive portion of the slurry having the objective to convert the material into a polishable condition. The slurry includes abrasive means in the form of colloidal abrasive small particles. The planarization of a semiconductor disk by CMP is an important step for the manufacture of plane defect-free and smooth semi-conductor disks. Frequently, the CMP process is the last processing step in the manufacturing line and considerably influences the shape and the surface qualities of the semiconductor disk which as known is the blank material for the manufacture of electrical, electronic and microelectronic components (prime wafer manufacture). Also after the coating of semi-conductor wafers, for example with an oxide, tungsten or other metal layer, a CMP machining takes place in order to provide the desired quality of the surface. In case this is not achieved, problems occur with lithographic processes in the form of focus failures by steps of focal field of the UV stepper or in form of disturbances of the conductor paths.
During the transport and the machining of the wafers the wafers are held by a carrier. The objective of such carrier is to transfer a homogenous pressure field or different pressure profiles to the back side of the wafers. Conventionally, the carrier is retained and moved by an apparatus whereby the carrier is rotated about a vertical axis and linearly moved in vertical and horizontal direction.
From DE 197 55 975 A1 a carrier has become known which is attached to a spindle or shaft which can be vertically moved. The carrier has a chuck plate at the lower side which through a universal joint is coupled with a support portion above the chuck plate. The chuck plate includes a plurality of bores which extend to the lower side of the chuck plate and which are connectable with a vacuum and/or a fluid source. The chuck plate is vertically movably guided by the support portion and an annular closed diaphragm is arranged between the support portion and the chuck plate, the diaphragm defining a sealed closed inner space which selectively can be connected to atmosphere, vacuum or a pressure source, respectively.
The objective of the invention is to provide chuck means for flat workpieces, in particular for wafers which enable a particular effective processing of the surfaces of the workpieces.
Similar to conventional chucks or carriers for semi-conductor wafers for the CMP polishing the invention provides a circular housing which is connected to a driving spindle or a shaft for rotation therewith. The housing includes a top wall and an annular side wall. The chuck plate is made of relatively rigid, however, elastically deformable material, for example of steel or plastic material and has ports at the lower side for the holding of wafers by vacuum. The chuck plate is floatingly arranged in the housing. It can freely move upwards and downwards and is laterally limited by a retainer ring which forms the side wall of the housing in the area of the chuck plate. A plurality of pressure chambers is provided above the chuck plate which have a desired shape and distribution. The pressure chambers can be concentrically arranged about the spindle axis and divided by radial walls. The pressure chambers are connected to a pressure manifold means which in turn is connected to a fluid source under pressure. By means of the pressure manifold means the pressure in the individual pressure chambers can be controlled. The pressure chambers have lower wall portions which are resilient, in particular flexible. The lower wall portions engage the upper side of the chuck plate and determine the pressure of the chuck plate onto the workpiece beyond the gravity force of the chuck plate if the workpiece lies on a polishing table. Thus, the polishing pressure of the chuck plate is solely determined by the pressure in the individual pressure chambers.
The transfer of the torque from the spindle to the chuck plate solely takes place though the frictional engagement of the lower chamber walls with the chuck plate.
The pressure force which is transferred from the pressure chamber to the chuck plate has the same value at any location in the pressure chamber. By the selection of the pressure in the pressure chambers the polishing result can be influenced.
The retainer ring at the housing can be splitted so that it can be easily released from the housing which allows the removal of the chuck plate. Frequently, a polishing cloth is adhered to the chuck plate. The cloth is a wear part and thus must be replaced from time to time. By the easy removal of the chuck plate, the replacement can be easily carried out at a remote location.
It is conceivable to have separate pressure conduits connected with the individual valves which are connected to the pressure chambers. The supply apparently has to take place through the spindle. Therefore, it is more simple and not particularly disadvantageous if only switching valves are associated with the pressure chambers which are connected to a common pressure control valve in order to generate selectively the pressure in desired pressure chambers. The pressure control valve can be located outside of the housing or the spindle, respectively, and connected to an axial passage within the spindle through a rotary duct. The passage in the spindle is connected to the individual switching valves in the housing. The switching valves are electrically controllable, with an external control device for the switching valves being connected to the switching valves through electrical conductors. The conductors could be connected to electrical lines within the spindle or the housing by sliding contact ring means associated with the spindle or the carrier. Also a contactless transmission can take place, e.g. through electromagnetic waves or infrared means.
It is conceivable to provide pressure control valves for the individual pressure chambers. However, small proportional valves which would be necessary, are not available.
The pressure chambers could be formed by a folded membrane which has upper and lower portions which alternate in radial direction. The upper portions can be connected to a plate within the housing, preferably through annular clamping rings so that the membrane rotates upon rotation of the spindle and the housing. The lower portions of the membrane have a larger thickness and engage the upper side of the chuck plate and transfer the torque onto the chuck plate through friction force. As the membrane is of an elastic material which has a small inherent rigidity, angle failures between the driving spindle and the polishing table and the polishing station can be compensated.
In the invention, the chuck plate can be formed as plane disk which can be deformed by means of the pressure chambers in the desired manner. The guidance of the chuck plate can be achieved by a cylindrical circumference of the plate which is guided by the housing or the mentioned retainer ring. To this purpose an annular groove can be formed at the circumference of the chuck plate, and a radially inwardly facing annular extension of the retaining ring can engage the groove in order to limit the vertical movement of the chuck plate.
The construction according to the invention can provide for a simple removal of the chuck plate as already described above. The passages of the chuck plate are connected to vacuum or a fluid source, respectively, through a passage in the spindle. Therefore, for this case the invention provides for a coupling which includes a part connected to the chuck plate and a part connected to the housing which in the coupled condition provides for a fluid connection to the passages in the chuck plate. The coupling must be structured such that the chuck plate can be easily released from the other coupling part in the housing after the retainer ring has been removed. As to this, a quick closure thread locking means is provided, e.g. formed by a helical groove in the coupling part secured to the housing, a projection of the coupling part connected to the chuck plate engaging the groove. By a respective rotation of the chuck plate, the coupling parts can be separated or coupled. By means of this construction the polishing cloth which is normally attached to the chuck plate can be easily removed from the chuck plate and replaced by another one.
The coupling part within the housing has to move with the vertical movement of the chuck plate, e.g. by its deformation but also by the vertical movement in operation. Therefore, this coupling part is vertically movable and preferably biased towards the chuck plate by means of a spring. A flexible conduit in the housing connects the coupling part in the housing with an axial passage in the spindle. Preferably, the coupling part within the housing consists of two portions, namely a first portion which forms a plug socket connection with a socket-like coupling part of the chuck plate and a second portion wherein the first portion is rotatably accommodated, however, secured against axial movement. The second portion is connected to a flexible conduit portion. The first portion is biased by a spring towards the chuck plate and is prevented from rotation in a lower position. If the first portion, however, is upwardly displaced after the coupling of the parts has taken place, the first portion can freely rotate. This is necessary because of the frictional transfer of the torque from the membrane to the chuck plate and a relative rotation between membrane and chuck plate may occur. Upon such relative rotation, the second portion of the second coupling part must not be rotated. The first portion, however, can freely rotate in the second portion so that no damages of the parts can occur.